The cotton plant in Egypt, studies in physiology and genetics . om them. Their rate of growthunder the same environmental conditions is slower thanthat of their tap-root; this phenomenon is one of thosecommonplaces of observation which have never received asatisfactory explanation. In spite of their slower growth,they produce an enormous increase in root area, on accountof their numbers, and if the soil is carefully washed awayfrom a cluster of cotton seedlings about six weeks aftersowing (Fig. 35), the root system appears as a tangledwhite gossamer web. Only a few of the rays of this websurvi
The cotton plant in Egypt, studies in physiology and genetics . om them. Their rate of growthunder the same environmental conditions is slower thanthat of their tap-root; this phenomenon is one of thosecommonplaces of observation which have never received asatisfactory explanation. In spite of their slower growth,they produce an enormous increase in root area, on accountof their numbers, and if the soil is carefully washed awayfrom a cluster of cotton seedlings about six weeks aftersowing (Fig. 35), the root system appears as a tangledwhite gossamer web. Only a few of the rays of this websurvive (Fig. 37). Before discussing the factors controlling root growth, wemay advert to the general form of the root-system, which,beginning as a vertical line, rapidly becomes an inverted * Audebeau. 34 THE COTTON PLANT IN EGYPT cone. AVheii plants are sown at wide intervals, this conicalform is maintained, the principal laterals extending radi-ally by the antumn to distances of over two metres Dec. 15th. or 8 months May Sid. S6 ^Pdays 7P days Soilurfacc. The new roots shown are those froma single lateral effects of asphyxiation, see sowingof March 28th. in Note:-S6 laterals,(with many tertiaries)on this one 36 days. Note:-Nolaterals. Fio. 35.—The Root : Development, Asphyxiation, and drawings from measurements. (Fig. 37); the irregular l^ase of the inverted cone thusbecomes al)out five metres in diameter, while its depthmay exceed two metres. When the plants are closely II DEVELOPMENT AND ENVIRONMENT 35 sown, iis ill the field crop, the uppermost hitenils fromadjacent phants l)egin to encroach on ea(^]i others territory,within three months from the date of sowing ; althoughinterlacing takes place, the form of the effective root-systemis modified by this lateral limitation into a cylindricalupper portion ending below in a cone. The depth of thecylindrical portion increases as lower and lower lateralscome progressively into con
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